Glycoconjugates are information-rich molecules that play diverse biological functions. The long-term interest of our research has been the study of biomedically useful glycosidase to understand: a) the pathogenesis of inborn errors of glycosphingolipid catabolism (sphingolipidoses), with emphasis on Tay-Sachs disease; and b) the structure and function of glycocojugates. Despite the available carrier- screening programs for Tay-Sachs disease, 50 new cases have been identified in the United States and Canada between 2000 and 2001. In addition, the mechanisms that lead to the overall clinical and neural manifestations of Tay-Sachs disease are still not well understood. Specific Aim 1 focuses on the biochemical studies of Tay-Sachs disease that includes: i) detailed analyses of glycosphingolipids and sphingolipid metabolites that specifically accumulate in the brains of Tay-Sachs patients and animal models of this disease; ii) studies of the level of taurine and tauro-GM2, the newly discovered GM2 derivative, in the pathological brain samples; iii) chemical synthesis of tauro-GM2 and studies of the pathophysiological significance of this novel GM2 derivative; and iv) studies of other biological functions of GM2 activator, an indispensable protein cofactor for the catabolism of Tay-Sachs ganglioside GM2. These studies should advance our understanding of pathogenic mechanisms of Tay-Sachs disease. Glycosidases play pivotal roles in our understanding of the structure, function and catabolism of glycoconjugates. Specific Aim 2 involves the studies of: i) a novel endo-beta-galactosidase capable of destroying blood group B antigenicity of type B red blood cells; ii) a KDN-sialidase capable of cleaving both KDN and NeuAc from sialogiycoconjugates and a KDNase that cleaves only KDN; and iii) an alpha-KDOase capable of cleaving KDO from endotoxins and a novel sialidase that cleaves the newly found sialosyl linkage. The novel endo-beta-galactosidase is potentially useful for converting type B red blood cells to type-neutral cells suitable for transfusion. These novel glycosidases will be useful for studying the structure and function of glycoconjugates. Our ultimate goal is to produce recombinant enzymes and make these biomedically useful glycosidases available to investigators in various fields.